If a backup is expired， which of the following is true？（）

A.  It can never be used for a restore/recover operation.

B.  Oracle will remove the backup set pieces from the flash recovery area.

C.  The backup has been used at least once to restore and recover the database.

D.  The backup is no longer valid because of a resetlogs operation.

E.  The physical backup set pieces are missing from the media.